236 FP, A. P. Barnard on the Zodiacal Light. 
pression, and the angle OML is the complement of HOP’. O 
being the centre of the circle of the horizon, and G_ that of 
the limiting circle, the depression enables us to find OL, GL. 
ML=OL.tan MOL; and GM= VYGL°+ML’?. Also, angle 
GML is easily found. Now the three planes make a solid angle 
at M, of which one of the containing plane angles (OML) is 
known, and also two of the inclinations; whence the angles 
an ML may be ascertained. Also, GMQ=GML+ 
LMQ: consequently, if a perpendicular, GL’, be dropped from 
G on MQ, its length may be found, and also the ordinate QL’, 
and the line L’M: whence QM is known. OM is found in the 
triangle OLM: and therefore, in the plane triangle OMQ, we 
have OM, MQ and the angle OMQ, from which to obtain the 
angle MOQ. This, and the known inclination of the plane 
OMQ to the horizon, enable us to determine the apparent alti- 
tude of Q. c 
This method has been applied to determine the aspect of the 
light as it would, under this supposition, appear in this latitude, 
at the close of twilight, when the inclination of the ecliptic to 
the horizon is at its minimum. The arch would follow the 
course of the ecliptic, froma point on the horizon 31° 20’ dis- 
tant in azimuth from the vertical passing through the sun, one 
hundred and forty-one degrees. The highest point of the arch 
uld be 32° above the horizon, and the extremity of the light 
would have an apparent altitude of 194°. There would also be 
a trace of the opposite cusp, rising about 2$° from the horizon. 
This being the appearance under the circumstances least favorable 
to visibility, at all other times both cusps ought to be seen, both 
morning and evening, throughout the year; and one of them 
ought always to have an enormous length when the sun is within 
18° of the horizon. 
These results being optical and geometrical necessities conse 
quent upon the hypothesis of a nebulous ring surrounding the 
earth and illuminated by the sun’s light, and being all of them 
unconfirmed by observation, it seems impossible to arrive at any 
other conclusion but that the hypothesis is untenable. 
e appear, therefore, to be conducted to one and the same, 
couclusion by the application to this theory of four distinct tests ; 
each one of them having no slight independent weight, and 4 
of them combined possessing an irresistible force. The zodiacal 
light must consequently be regarded as presenting a problem stil 
unsolved. The observations of Mr. Jones, when published, maY 
possibly present some clew to the mystery which has not yet 
een detected in them. But whatever else they may show, the 
| Writer cannot but believe that they will furnish, 1n them- 
